1. Field of the Invention
The present invention generally relates to internal combustion engines, and more particularly, to a method of reducing emissions in a two-stroke sliding vane engine wherein the vanes slide with either a radial or axial component of vane motion.
2. Description of the Related Art
The overall invention relates to the class of devices known as internal combustion engines. Internal combustion engines produce mechanical power from the chemical energy contained in the fuel, this energy being released by burning or oxidizing the fuel internally, within the engine's structure.
However, the oxidation of hydrocarbon fuels at the elevated temperatures and pressures associated with internal combustion engines produce at least three major pollutant types:
(1) Oxides of Nitrogen (NO.sub.x) PA1 (2) Oxides of Carbon (CO, CO.sub.2) PA1 (3) Hydrocarbons (HC) PA1 (1) lower peak combustion temperatures; PA1 (2) extended combustion duration; and PA1 (3) leaner fuel-air ratio. PA1 (1) inducting fresh air into a vane cell; PA1 (2) injecting fuel into the vane cell at an ultra-lean equivalence ratio less than 0.65 and at a location such that the circumferential distance at mid-cell-height to an ultra-lean combustion-initiating device (hereafter "U.C.D.") is at least about 4 times the vane cell height at intake; PA1 (3) compressing the ultra-lean fuel-air combination while mixing to a dimensionless concentration fraction of less than 0.25; PA1 (4) combusting the ultra-lean, mixed fuel-air combination after first communication with the U.C.D.; PA1 (5) scavenging the combusted fuel-air combination after an expansion cycle.
Carbon dioxide (CO.sub.2) is a non-toxic necessary by-product of the hydrocarbon combustion process and can only be effectively reduced in absolute output by increasing the overall efficiency of the engine for a given application. The major pollutants NO.sub.x, CO, and HC contribute significantly to global pollution and are usually the pollutants referred to in engine discussions. Other pollutants, such as aldehydes associated with alcohol fuels and particulate associated with diesel engines, contribute to global pollution as well. In the last decade it has become clear that the reduction of all such pollutants is of global importance; providing an impetus for advanced research in pollution chemistry and engine design.
Production engine devices currently include piston engines, Wankel rotary engines, and turbine engines, which may be divided into two fundamental categories: positive displacement engines and turbine engines.
In positive displacement engines (piston and Wankel engines) the flow of the fuel-air mixture is segmented into distinct volumes that are completely or almost completely isolated by solid sealing elements throughout the engine cycle, creating compression and expansion through physical volume changes within a chamber.
Turbine engines, on the other hand, rely on fluid inertia effects to create compression and expansion, without solidly isolating chambers of the fuel-air mixture. Regarding pollution emissions, turbine engines have to date offered three advantageous features in most applications:
Because of these three features, pollution emissions of NO.sub.x, CO, and HC are normally lower in a turbine engine than in a piston or Wankel engine. The significantly lower peak combustion temperatures--largely provided by the leaner fuel-air ratio--reduce NO.sub.x emissions by reducing the rate of formation of NO.sub.x, while the extended combustion duration and leaner fuel-air ratio reduce CO and HC emissions through oxidation of these compounds.
However, one feature of turbines has limited the magnitude of NO.sub.x reduction in most designs until recently, namely that the fuel and air are not adequately mixed prior to combustion. Even if the average peak combustion temperature is low, inadequate mixing prior to combustion will significantly limit the degree of NO.sub.x reduction, an effect seen in conventional diesel and turbine engines and explained in the specification below.
Certain recent developments in the field of gas turbines, such as the turbine engines incorporating the "Double-Cone" burner, provide sophisticated means to allow adequate premixing of fuel and air prior to combustion, and have in actual production proven the validity of the theories supporting premixing as important to reducing NO.sub.x emissions. Thus, designs have been recently developed within the gas turbine engine field which simultaneously reduce NO.sub.x, CO, and HC emissions to less than 25 parts per million each without catalytic exhaust treatment, or roughly a factor of 100 below the modern spark ignition piston engine.
Turbine engines, however, are not practical for most mainstream applications (e.g. automobiles) because of high cost, poor partial power performance, and/or low efficiency at small sizes, leaving positive displacement engines such as the piston and Wankel designs for these applications.
Commercially available piston and Wankel designs offer poor emissions performance and/or require catalytic converters to reduce emissions. Even with catalytic converters, pollutant output is substantially higher than desired, being on the order of several hundred to several thousand parts per million of NO.sub.x, CO, and HC for most applications. In addition to high cost, a major drawback of the use of catalytic converters is that their effectiveness weakens over time, requiring inspection and replacement to maintain performance.
In light of the foregoing, there exists a need for a method of reducing emissions in a positive displacement engine towards the scale of the aforementioned advanced turbine engines, but without the need for catalytic converters.